Extensive research results concerning the lachrymatory factor that is generated when onions are crushed or cut have been reported in the past, and it is now believed that this lachrymatory factor is produced when S-1-propenyl-cysteine sulfoxide is degraded by aliinase.
However, according to research conducted by the present inventors, lachrymatory factor is not produced merely as a result of S-1-propenyl-cysteine sulfoxide being broken down by aliinase; the participation of other enzymes (lachrymatory factor producing enzymes) is indispensable.
Accordingly, as a result of diligent research, the present inventors developed a method of producing lachrymatory factor producing enzyme (an enzyme that produces a lachrymatory substance), and also clarified the physico-chemical properties of this lachrymatory factor producing enzyme; the inventors have previously field a patent application (Japanese Patent Application Laid-Open No. H10-295373) relating to this method.
Specifically, extensive research results regarding the formation and decomposition of the lachrymatory factor (LF) that is present in onions and the like have been reported in the past. However, in regard to the production mechanism of the abovementioned lachrymatory factor, it was believed in the past that the enzyme aliinase acts on the abovementioned precursor substance (PeCSO), and that a stable lachrymatory factor is formed non-enzymatically via sulfenic acid. On the other hand, research conducted by the present inventors has demonstrated that the abovementioned factor is actually not produced by the action of the enzyme aliinase alone, and that the participation of other enzymes is indispensable.
Accordingly, as a result of further diligent research, the present inventors discovered the existence of a new enzyme (lachrymatory factor producing enzyme) that apparently produces lachrymatory factor by isomerizing the abovementioned sulfenic acid. As a result, it was found that the abovementioned precursor substance is converted into lachrymatory factor (an aromatic component) or a different flavoring component depending on the action of the enzyme involved.
By using the amino acid sequence of this lachrymatory factor producing enzyme, and the DNA information that codes for this amino acid sequence, it is possible to achieve effect genetic recombination, mutation breeding, cross breeding and the like in the development of varieties of onions; this is useful for producing onions that tend not to generate lachrymatory factor even when crushed or cut.
Meanwhile, by utilizing DNA information that codes for the amino acid sequence of this lachrymatory factor producing enzyme, it is possible to produce this enzyme in large quantities by means of genetic recombination techniques and the like. For example, this is useful for the development of techniques for the efficient production of lachrymatory factor, which is useful in the treatment of alacrima (dry eye) and the like.
However, there have been absolutely no examples in the past of reports relating to the amino acid sequence of lachrymatory factor producing enzyme, or the DNA that codes for this amino acid sequence, so that no information has been available. As a result, research at the genetic level concerning lachrymatory factor producing enzyme has been difficult.